1. Field of the Invention
This invention relates to a chair, in particular a work or office chair, having a seat, which is placed on a chair frame and can be tilted in a front area around a horizontal pivot shaft, which can be moved up and down on a spatial guide curve in relation to the chair frame, and which is hingedly connected to a rocker extending toward the rear from an articulated rocker bearing fixed on the chair frame and is thereafter spaced apart from the seat rear edge, or is laterally guided upward next to the seat. The chair also has a backrest coupled to the upward guided section of the rocker, with a tilt that is forcibly changed superproportionally when the tilting of the seat is changed.
2. Discussion of Related Art
An office chair is known from German Patent Reference DE 39 16 474 C2. With this known chair, the front end section of a rocker-like pivot lever extending under the seat is tiltably fastened on a bearing bracket of the chair frame, while a section, which is spaced apart from the rear edge of the seat and leads upward, supports the back rest.
In a front area the seat is placed on a horizontal pivot shaft which, when the seat is tilted toward the rear, is moved together with it downward and backward, while at the same time the backrest is superproportionally tilted toward the rear. With its section extending underneath the seat, the pivot lever is also connected via an intermediate piece with the underside of the seat between the center and rear areas of the latter. When tilting the seat and the backrest, the distance between the rear edge of the seat and the lower edge of the backrest remains substantially the same, so that a so-called shirt-pulling effect is prevented to a large extent. Pressure on the backs of the knees is also avoided, because the backward tilting of the seat the front of the seat simultaneously moves downward.
Another chair with a synchronization mechanism between the seat and the backrest is disclosed by German Patent Reference DE 87 13 972 U1.
With such synchronization mechanisms for the simultaneous movement of the seat and the back, applicable specifications cite a transmission ratio in the range between 1.5 and 3.5. With customary chairs of the above mentioned type an opening angle range between the seat and the backrest of 87xc2x0 to 110xc2x0, for example, is achieved. Larger backward tilts, in particular of the backrest, are desired at many work stations, for example air traffic control centers or PC work stations, but cannot be satisfactorily achieved by present synchronization mechanisms, because sequence errors occur at larger opening angles, for example relative movements between the back and the backrest that are too large, so that a shirt-pushing effect occurs. A wrong synchronization ratio between the backrest and the seat is present, increasing a distance of the lower backrest area from the pelvis, so that an ergonomically disadvantageous gap occurs because of the pelvis rolling back, and sinking the lower backrest edge during backward tilt, so that a continuous seat surface is not achieved.
One object of this invention is to provide a chair of the type mentioned above but which provides an improved sequence control of the synchronous movement between the seat and the backrest, along with the possibility of larger opening angles, and therefore tilt angles of the backrest toward the back.
This object is achieved with this invention according to the characteristics set forth in this specification and in the claims. In one embodiment, the backrest is hingedly coupled with the rocker via a coupling point, and the seat is additionally coupled with the backrest via a control lever arrangement, by which the backrest is tilted backward with respect to the rocker when the seat is tilted backward. With the articulated coupling of the backrest with the rocker and because of the control lever arrangement, the backrest can also be tilted with respect to the rocker during the tilt movement, so that a larger opening angle between the seat and the backrest, along with an even and exactly controllable sequential movement, is achieved. During this, the pelvis is supported by the lower backrest area over the entire course of the tilting, wherein a shirt-pushing effect is prevented even at large angles of tilt and a feeling of pleasant seating is conveyed. An easily attainable opening range lies, for example, between at least 87xc2x0 to 120xc2x0.
For bringing the seat and the backrest into the active, forward oriented work position the structure can have a rocker bearing with a torsion rod, which prestresses the rocker against a setting limitation, which limits its tilting position toward the front. An advantageous structure for achieving the synchronization movement at a large opening angle range is assisted if the control lever arrangement has a lever, which is articulated on the upward guided section of the rocker at a joint location below the coupling point, which is hingedly coupled with an upper lever section via a connecting point with the backrest, and is hingedly coupled with a lower lever section with the rear area of the seat. A coupling piece hingedly connected at a lever connection point of the lower lever section, and at a seat connection point of the rear area of the seat, also help provide an accurate control, along with a simple construction.
In one embodiment, a measure for connecting the seat to the lever arrangement includes a lower seat element projecting past the rear edge of a seat support and the control lever arrangement connected to the projecting section of the lower seat element. Alternatively, the control lever arrangement can be connected to the lower seat element, beneath or at the side of the seat.
For example, the placement of the chair backrest for performing the synchronized tilt movement is simply achieved with a backrest rocker provided by two articulated connections at the ends for connecting the chair backrest to the upward guided section of the rocker, or at least one articulated connection is replaced by a thrust linkage.
A dependable tilted placement of the seat is achieved because, for connecting the seat with the chair frame, seat rockers are arranged on both sides underneath the front area of the seat, one end of which is hingedly placed on the pivot shaft and the other on the front area of the chair frame, or a thrust linkage is provided in the frontal seat area. It is advantageous if the seat rockers are arranged so that their ends facing the pivot shaft move downward when the seat is tilted back.
The measure by which the seat is connected between its center and rear areas with a connecting piece, or hingedly directly with the rocker, also helps achieve the synchronous movement.
A stable placement of the seat and the backrest are aided because two lateral rocker elements are provided, which are connected with each other by at least one cross brace and whose one, forward projecting section extends at a distance underneath the seat, or laterally thereof, while its upward extending section is spaced apart from the back of the backrest, or laterally thereof. For example, in this embodiment the rocker extends upward in the front lateral seat area and then toward the rear, and can be embodied as an armrest on both sides. In connection with this, the control of the synchronous movement can be simply achieved because the control lever arrangement extends in an approximately center vertical plane between the two rocker elements and is also spaced apart from the back of the backrest.
Moreover, an advantageous play-free movement is accomplished with a spring force that is effective in the pulling direction between the articulated connecting point and the articulated connecting point at the rocker.
An ergonomically advantageous support of the head is achieved with head support coupled to an extension, which projects past the upper edge of the backrest, of a lever mechanism for the synchronous adjustment of the seat and the backrest. The lever mechanism is embodied so that, when the backrest is tilted back, the head support is tilted back over a narrower tilt angle than the backrest. Because of the relative movement between the head support and the backrest, the head is guided forward during increasing tilt, and the neck muscles are relieved, while the field of view is maintained. To simply achieve this, there is a rigid or hingedly connected, mechanically controlled extension portion, of the rocker.
An adjustment possibility for the tilting of the backrest results from the coupling element being length-adjustable.
The lever can be manually released because it is connected with the rear area of the seat by a manually actuable adjusting element.
A conventional synchronization mechanism can be realized by removing the coupling rod and locking the backrest joints.